Other
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmgp33a..02e&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #GP33A-02
Other
1513 Geomagnetic Excursions, 1520 Magnetostratigraphy, 1530 Rapid Time Variations
Scientific paper
Cryptochrons are short geomagnetic events (less than about 30 k.y. in duration) that are caused by large changes in the direction and/or intensity of the geomagnetic field. As such, they may equate to paleointensity fluctuations, geomagnetic excursions, or full polarity reversals that have durations less than that of a subchron. Their existence was first recognized by Cande and Kent (1992) by the "tiny wiggles" that they caused in marine magnetic anomaly profiles. Since then, our ability to document and study these and other forms of short-term geomagnetic field variability has been greatly enhanced by the recovery of long, continuous sedimentary sections from the World's oceans. The Ocean Drilling Program (ODP) and its successor, the Integrated Ocean Drilling Program (IODP), have played a crucial role in this effort, not only in acquiring the necessary cores but also in supporting the scientific community as they have developed new sampling strategies, stratigraphic analysis tools, and instrumentation. In particular, coring multiple holes at a site has allowed the construction of composite sections that yield stratigraphically complete records. Continuous, high-resolution measurements, made possible by automated-track systems, has provided the necessary quantity and quality of data to resolve the age, duration, and geomagnetic characteristics of several of the cryptochrons that had previously only be observed in marine magnetic anomaly profiles. We will discuss the geomagnetic changes associated with eight cryptochrons that occur in the Miocene and Plio- Pleistocene. We will also examine intervals in the Paleocene, Eocene, and Oligocene where cryptochrons were expected based on marine magnetic anomaly profiles but where marine sedimentary sections fail to record any notable changes in direction. This may indicate that the events are too short-lived to be recorded in the lower sedimentation rate records from these older time periods or that the cryptochrons are due only to fluctuations in the intensity of the field and not directional changes.
Acton Gary D.
Evans Helen F.
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